Method for preparing synthesis gas and aromatic hydrocarbon

ABSTRACT

Provided is a method for preparing synthesis gas and aromatic hydrocarbons, and more particularly, a method for preparing synthesis gas and aromatic hydrocarbons including: supplying a pyrolysis fuel oil (PFO) stream containing PFO and a pyrolysis gas oil (PGO) stream containing PGO to a distillation tower as a feed stream (S10), the PFO stream and the PGO stream being discharged in a naphtha cracking center (NCC) process; and supplying a lower discharge stream from the distillation tower to a combustion chamber for a gasification process and supplying an upper discharge stream from the distillation tower to a BTX preparation process (S20).

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a National Phase entry pursuant to 35 U.S.C.§ 371 of International Application No. PCT/KR2021/018817, filed on Dec.11, 2021, and claims the benefit of and priority to Korean PatentApplication No. 10-2021-0082382, filed on Jun. 24, 2021, the entirecontents of which are incorporated by reference in their entirety forall purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a method for preparing synthesis gasand aromatic hydrocarbons, and more particularly, to a method for usingpyrolysis fuel oil discharged from a gasoline fractionator in a naphthacracking center (NCC) process as a raw material for a gasificationprocess and recovering aromatic hydrocarbons in the pyrolysis fuel oil.

BACKGROUND ART

A naphtha cracking center (hereinafter, referred to as NCC) process is aprocess of cracking naphtha that is a gasoline fraction at a temperatureof about 950° C. to 1,050° C. to produce ethylene, propylene, butylene,and benzene, toluene, and xylene (BTX) that are basic raw materials fora petrochemical product.

In the related art, benzene, toluene, xylene, and styrene have beenprepared using raw pyrolysis gasoline (RPG) that is a by-productproduced in a process of producing ethylene and propylene using naphthaas a raw material, and pyrolysis fuel oil (PFO) has been used as a fuel.However, since the pyrolysis fuel oil has a high content of sulfur and ahigh carbon dioxide (CO₂) emission factor for use as a fuel without apretreatment, the market is getting smaller due to the environmentalregulations and a situation where sales are impossible in the futureshould be prepared for.

Meanwhile, synthesis gas (syngas) is artificially prepared gas, unlikenatural gas such as naturally derived gas, methane gas, or ethane gasthat is ejected from the land in oil fields and coal fields, and isprepared by a gasification process.

The gasification process is a process of converting a hydrocarbon suchas coal, petroleum, or biomass as a raw material into synthesis gasmainly composed of hydrogen and carbon monoxide by pyrolysis or achemical reaction with a gasifying agent such as oxygen, air, or watervapor. A gasifying agent and a raw material are supplied to a combustionchamber positioned at the foremost end of the gasification process toproduce synthesis gas by a combustion process at a temperature of 700°C. or higher, and as a kinematic viscosity of the raw material suppliedto the combustion chamber is higher, a differential pressure in thecombustion chamber is increased or atomization is not smoothlyperformed, which causes deterioration of combustion performance or anincrease in risk of explosion due to excessive oxygen.

In the related art, as a raw material for a gasification process forpreparing synthesis gas using a liquid phase hydrocarbon raw material,refinery residues, such as vacuum residues (VR) and bunker-C oil,discharged from a refinery where crude oil is refined have been mainlyused. However, since the refinery residue has a high kinematicviscosity, a pretreatment such as a heat treatment or addition of adiluent or water is required to use the refinery residue as the rawmaterial for the gasification process, and since the refinery residuehas high contents of sulfur and nitrogen, production of acidic gas suchas hydrogen sulfide and ammonia is increased during the gasificationprocess. Thus, in order to respond to tightened environmentalregulations, a need to replace the refinery residue with a raw materialhaving low contents of sulfur and nitrogen has been raised.

Accordingly, a method for using the pyrolysis fuel oil as a raw materialfor a gasification process has been considered. However, in order to usethe pyrolysis fuel oil as the raw material for the gasification process,the pyrolysis fuel oil should be heated to lower a kinematic viscositythereof, but it is difficult to satisfy a kinematic viscosity conditionfor use of the pyrolysis fuel oil as the raw material for thegasification process at a flash point or lower due to a significantlyhigh kinematic viscosity of the pyrolysis fuel oil.

Therefore, the present inventors have found that when the pyrolysis fueloil (PFO) in the naphtha cracking center (NCC) process is used as theraw material for the gasification process, greenhouse gas emissions maybe reduced, operating costs of the gasification process may be reduced,and process efficiency may be improved, as compared with the case ofusing the refinery residue as a raw material according to the relatedart, thereby completing the present invention.

The background description provided herein is for the purpose ofgenerally presenting context of the disclosure. Unless otherwiseindicated herein, the materials described in this section are not priorart to the claims in this application and are not admitted to be priorart, or suggestions of the prior art, by inclusion in this section.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method for preparingsynthesis gas by which greenhouse gas emissions may be reduced,operating costs of a gasification process may be reduced, and processefficiency may be improved, as compared with the case of using arefinery residue as a raw material according to the related art, byusing pyrolysis fuel oil (PFO) discharged in a naphtha cracking center(NCC) process as the raw material for the gasification process.

Technical Solution

In one general aspect, a method for preparing synthesis gas and aromatichydrocarbons includes: supplying a pyrolysis fuel oil (PFO) streamcontaining PFO and a pyrolysis gas oil (PGO) stream containing PGO to adistillation tower as a feed stream (S10), the PFO stream and the PGOstream being discharged from a naphtha cracking center (NCC) process;and supplying a lower discharge stream from the distillation tower to acombustion chamber for a gasification process to obtain synthesis gasand supplying an upper discharge stream from the distillation tower to aBTX preparation process (S20) to obtain aromatic hydrocarbons.

Advantageous Effects

According to the present invention, the pyrolysis fuel oil (PFO) and thepyrolysis gas oil (PGO) in the naphtha cracking center (NCC) process arepretreated and used as the raw material for the gasification process,such that greenhouse gas emissions may be reduced, operating costs ofthe gasification process may be reduced, and process efficiency may beimproved, as compared with the case of using the refinery residue as theraw material according to the related art.

In addition, light pyrolysis fuel oil generated during the process ofpretreating the pyrolysis fuel oil (PFO) and the pyrolysis gas oil (PGO)are used as raw materials for preparing BTX together with the rawpyrolysis gasoline (RPG), such that production of the BTX may beincreased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow diagram for a method for preparing synthesisgas and aromatic hydrocarbons according to an exemplary embodiment ofthe present invention.

FIG. 2 is a process flow diagram for a method for preparing synthesisgas and aromatic hydrocarbons according to Comparative Example 1 of thepresent invention.

FIG. 3 is a process flow diagram for a method for preparing synthesisgas and aromatic hydrocarbons according to Comparative Example 2 of thepresent invention.

FIG. 4 is a process flow diagram for a method for preparing synthesisgas and aromatic hydrocarbons according to Comparative Example 3 of thepresent invention.

DETAILED DESCRIPTION

The terms and words used in the description and claims of the presentinvention are not to be construed limitedly as having general ordictionary meanings but are to be construed as having meanings andconcepts meeting the technical ideas of the present invention, based ona principle that the inventors are able to appropriately define theconcepts of terms in order to describe their own inventions in the bestmode.

The term “stream” in the present invention may refer to a flow of afluid in a process, or may refer to a fluid itself flowing in a pipe.Specifically, the “stream” may refer to both a fluid itself flowing in apipe connecting respective apparatuses to each other and a flow of afluid. In addition, the fluid may refer to a gas or liquid, and a casein which a solid substance is included in the fluid is not excluded.

In the present invention, the term “C#” in which “#” is a positiveinteger represents all hydrocarbons having # carbon atoms. Therefore,the term “C8” represents a hydrocarbon compound having 8 carbon atoms.In addition, the term “C#−” represents all hydrocarbon molecules having# or fewer carbon atoms. Therefore, the term “C8-” represents ahydrocarbon compound having 8 or fewer carbon atoms. In addition, theterm “C#+” represents all hydrocarbon molecules having # or more carbonatoms. Therefore, the term “C10+” represents a hydrocarbon compoundhaving 10 or more carbon atoms.

Hereinafter, the present invention will be described in more detail withreference to FIG. 1 in order to assist in the understanding of thepresent invention.

According to the present invention, there is provided a method forpreparing synthesis gas (syngas) and aromatic hydrocarbons. The methodfor preparing synthesis gas and aromatic hydrocarbons may include:supplying a pyrolysis fuel oil (PFO) stream containing PFO and apyrolysis gas oil (PGO) stream containing PGO to a distillation tower 50as a feed stream (S10), the PFO stream and the PGO stream beingdischarged in a naphtha cracking center process (S1); and supplying alower discharge stream from the distillation tower 50 to a combustionchamber for a gasification process (S3) and supplying an upper dischargestream from the distillation tower 50 to a BTX preparation process (S4)(S20).

The synthesis gas is artificially prepared gas, unlike natural gas suchas naturally derived gas, methane gas, or ethane gas that is ejectedfrom the land in oil fields and coal fields, and is prepared by thegasification process.

The gasification process is a process of converting a hydrocarbon suchas coal, petroleum, or biomass as a raw material into synthesis gasmainly containing hydrogen and carbon monoxide by pyrolysis or achemical reaction with a gasifying agent such as oxygen, air, or watervapor. Specifically, in the present invention, the synthesis gas maycontain hydrogen and carbon monoxide. A gasifying agent and a rawmaterial are supplied to a combustion chamber positioned at the foremostend of the gasification process to produce synthesis gas by a combustionprocess at a temperature of 700° C. or higher, and as a kinematicviscosity of the raw material supplied to the combustion chamber ishigher, a differential pressure in the combustion chamber is increasedor atomization is not smoothly performed, which causes deterioration ofcombustion performance or an increase in risk of explosion due toexcessive oxygen.

In the related art, as a raw material for a gasification process forpreparing synthesis gas using a liquid phase hydrocarbon raw material,refinery residues, such as vacuum residues (VR) and bunker-C oil,discharged from a refinery where crude oil is refined have been mainlyused. However, since the refinery residue has a high kinematicviscosity, a pretreatment such as a heat treatment or addition of adiluent or water is required to use the refinery residue as the rawmaterial for the gasification process, and since the refinery residuehas high contents of sulfur and nitrogen, production of acidic gas suchas hydrogen sulfide and ammonia is increased during the gasificationprocess. Thus, in order to respond to tightened environmentalregulations, a need to replace the refinery residue with a raw materialhaving low contents of sulfur and nitrogen has been raised. For example,among the refinery residues, a vacuum residue may contain about 3.5 wt %of sulfur and about 3,600 ppm of nitrogen, and bunker C-oil may containabout 4.5 wt % of sulfur.

Meanwhile, pyrolysis fuel oil (PFO) discharged in a naphtha crackingcenter process that is a process of cracking naphtha to preparepetrochemical basic materials such as ethylene and propylene isgenerally used as a fuel. However, since the pyrolysis fuel oil has ahigh content of sulfur for use as a fuel without a pretreatment, themarket is getting smaller due to the environmental regulations and asituation where sales are impossible in the future should be preparedfor.

Accordingly, a method for using the pyrolysis fuel oil as a raw materialfor a gasification process has been considered. However, in order to usethe pyrolysis fuel oil as the raw material for the gasification process,the pyrolysis fuel oil should be heated to lower a kinematic viscositythereof, but it is difficult to satisfy a kinematic viscosity conditionfor use of the pyrolysis fuel oil as the raw material for thegasification process at a flash point or lower due to a significantlyhigh kinematic viscosity of the pyrolysis fuel oil.

Accordingly, the present invention is intended to reduce greenhouse gasemissions, to reduce operating costs of a gasification process, and toimprove process efficiency, as compared with the case of using arefinery residue as a raw material according to the related art, bydeveloping a pretreatment process (S2) for using the pyrolysis fuel oil(PFO) stream containing PFO and the pyrolysis gas oil (PGO) streamcontaining PGO that are discharged in the naphtha cracking centerprocess as the raw materials for the gasification process. In addition,a light PFO stream discharged in the pretreatment process (S2) isrecovered to prepare aromatic hydrocarbons, such that production of thearomatic hydrocarbons may be increased.

According to an exemplary embodiment of the present invention, the rawpyrolysis gasoline (RPG) stream containing RPG, the pyrolysis fuel oil(PFO) stream containing PFO, and the pyrolysis gas oil (PGO) streamcontaining PGO may be discharged in the naphtha cracking center process(S1).

Specifically, the naphtha cracking center process is a process ofcracking naphtha containing paraffin, naphthene, and an aromaticcompound (aromatics) to produce ethylene, propylene, butylene, andbenzene, toluene, and xylene (BTX) used as petrochemical basicmaterials, and the naphtha cracking center process may be largelycomposed of a cracking process, a quenching process, a compressionprocess, and a refining process.

The cracking process is a process of cracking naphtha into hydrocarbonshaving fewer carbon atoms in a cracking furnace at 800° C. or higher,and may discharge cracked gas at a high temperature. Here, the naphthamay be subjected to a preheating process with high pressure water vaporbefore entering the cracking furnace, and then, the preheated naphthamay be supplied to the cracking furnace.

The quenching process is a process of cooling the cracked gas at a hightemperature, for suppressing a polymerization reaction of hydrocarbonsin the cracked gas at a high temperature discharged from the crackingfurnace, recovering waste heat, and decreasing a heat load in asubsequent process (compression process). Here, the quenching processmay include primary cooling of the cracked gas at a high temperaturewith quench oil and secondary cooling with quench water.

Specifically, in the primary cooling, the cracked gas may be supplied toa gasoline fractionator to separate light oil containing hydrogen,methane, ethylene, propylene, and the like, the raw pyrolysis gasoline(RPG), the pyrolysis fuel oil (PFO), and the pyrolysis gas oil (PGO)from the cracked gas. Thereafter, the light oil may be transported to asubsequent compression process.

The compression process may be a process of producing compressed gashaving a reduced volume by elevating a pressure of the light oil under ahigh pressure for economically separating and refining the light oil.

The refining process is a process of cooling the compressed gas which iscompressed with a high pressure to a cryogenic temperature and thenseparating components in stages by a boiling point difference, and mayproduce hydrogen, ethylene, propylene, propane, C4 oil, raw pyrolysisgasoline (RPG), and the like.

As described above, in the quenching process in the naphtha crackingcenter process (S1), the raw pyrolysis gasoline (RPG), the pyrolysisfuel oil (PFO), and the pyrolysis gas oil (PGO) may be discharged. Ingeneral, the pyrolysis fuel oil (PFO) contains about 0.1 wt % or less ofsulfur and about 20 ppm or less of nitrogen, and when it is used as afuel, sulfur oxides (SOx) and nitrogen oxides (NOx) are dischargedduring a combustion process, and thus, environmental issues may beraised. However, in a case where the pyrolysis fuel oil (PFO) is used asa raw material of synthesis gas, the environmental issues are quitesmall.

Accordingly, in the present invention, the above problems may be solvedby pretreating the pyrolysis fuel oil (PFO) and the pyrolysis gas oil(PGO) by the pretreatment process (S2) and using them as the rawmaterials for the gasification process for preparing synthesis gas, andgreenhouse gas emissions may be reduced, operating costs of thegasification process may be reduced, and process efficiency may beimproved, as compared with the case of using the refinery residue as theraw material for the gasification process according to the related art.In addition, a light PFO stream discharged in the pretreatment process(S2) is used as a raw material for preparing aromatic hydrocarbons, suchthat production of the aromatic hydrocarbons may be increased.

According to an exemplary embodiment of the present invention, the PFOstream and the PGO stream of the present invention may contain pyrolysisfuel oil (PFO) and pyrolysis gas oil (PGO) discharged from a gasolinefractionator 10 in the naphtha cracking center process (S1),respectively. As a specific example, in the total number of stages ofthe gasoline fractionator 10, when a top stage is expressed as a stageof 1% and a bottom stage is expressed as a stage of 100%, the pyrolysisfuel oil (PFO) may be discharged at a stage of 90% or more, 95% or more,or 95% to 100%, of the total number of stages of the gasolinefractionator 10. In addition, the pyrolysis gas oil (PGO) may bedischarged at a stage of 10% to 70%, 15% to 65%, or 20% to 60%, of thetotal number of stages of the gasoline fractionator 10. For example,when the total number of stages of the gasoline fractionator 10 is 100,a top stage may be the first stage and a bottom stage may be the100^(th) stage, and a stage of 90% or more of the total number of stagesof the gasoline fractionator 10 may refer to the 90^(th) stage to the100^(th) stage of the gasoline fractionator 10.

The PGO stream is discharged from a side portion of the gasolinefractionator 10 in the naphtha cracking center process (S1) and may be alower discharge stream which is discharged from a lower portion of afirst stripper 20 after supplying a side discharge stream containing thepyrolysis gas oil (PGO) to the first stripper 20. In addition, the PFOstream is discharged from a lower portion of the gasoline fractionator10 in the naphtha cracking center process (S1) and may be a lowerdischarge stream which is discharged from a lower portion of a secondstripper 30 after supplying a lower discharge stream containing thepyrolysis fuel oil (PFO) to the second stripper 30.

The first stripper 20 and the second stripper 30 may be devices in whicha stripping process of separating and removing gas or vapor dissolved ina liquid is performed, and may be performed by methods such as directcontact, heating, and pressurization by, for example, steam, inert gas,or the like. As a specific example, the side discharge stream from thegasoline fractionator 10 is supplied to the first stripper 20, such thatan upper discharge stream containing a light fraction separated from theside discharge stream from the gasoline fractionator 10 may be refluxedfrom the first stripper 20 to the gasoline fractionator 10. In addition,the lower discharge stream from the gasoline fractionator 10 is suppliedto the second stripper 30, such that an upper discharge streamcontaining a light fraction separated from the lower discharge streamfrom the gasoline fractionator 10 may be refluxed from the secondstripper 30 to the gasoline fractionator 10.

According to an exemplary embodiment of the present invention, the PGOstream may contain 70 wt % or more or 70 wt % to 95 wt % of C10 to C12hydrocarbons, and the PFO stream may contain 70 wt % or more or 70 wt %to 98 wt % of C13+ hydrocarbons. For example, the PGO stream containing70 wt % or more of C10 to C12 hydrocarbons may have a kinematicviscosity at 40° C. of 1 to 200 cSt and a flash point of 10 to 50° C. Inaddition, for example, the PFO stream containing 70 wt % or more of C13+hydrocarbons may have a kinematic viscosity at 40° C. of 400 to 100,000cSt and a flash point of 70 to 200° C. As such, the PFO streamcontaining more heavy hydrocarbons than the PGO stream may have a higherkinematic viscosity and a higher flash point than the pyrolysis gas oilunder the same temperature conditions.

According to an exemplary embodiment of the present invention, a boilingpoint of the PGO stream may be 200 to 288° C. or 210 to 270° C., and aboiling point of the PFO stream may be 289° C. to 550° C. or 300 to 500°C.

The boiling points of the PGO stream and the PFO stream may refer toboiling points of a PGO stream and a PFO stream in a bulk form, eachcomposed of a plurality of hydrocarbons. Here, the types of hydrocarbonscontained in the PGO stream and the types of hydrocarbons contained inthe PFO stream may be different from each other, and some types may bethe same as each other. As a specific example, the types of hydrocarbonscontained in the PGO stream and the PFO stream may be included asdescribed above.

According to an exemplary embodiment of the present invention, the rawpyrolysis gasoline (RPG) stream containing RPG discharged from thegasoline fractionator 10 in the naphtha cracking center process (S1) maybe supplied to the BTX preparation process (S4). As a specific example,the raw pyrolysis gasoline (RPG) may be discharged at a stage of 5% orless or 1% to 5%, of the total number of stages of the gasolinefractionator 10.

The RPG stream is discharged from an upper portion of the gasolinefractionator 10 in the naphtha cracking center process (S1). The upperdischarge stream containing the raw pyrolysis gasoline (RPG) may besupplied to an NCC subsequent process (not illustrated) to removehydrogen and C4− hydrocarbon substances, thereby separating the RPGstream.

The RPG stream may be a C5+ hydrocarbon mixture, and specifically, maybe a mixture in which C5 hydrocarbons to C10 hydrocarbons are rich. Forexample, the RPG stream may include one or more selected from the groupconsisting of iso-pentane, n-pentane, 1,4-pentadiene, dimethylacetylene,1-pentene, 3-methyl-1-butene, 2-methyl-1-butene, 2-methyl-2-butene,iso-prene, trans-2-pentene, cis-2-pentene, trans-1,3-pentadiene,cyclopentadiene, cyclopentane, cyclopentene, n-hexane, cyclohexane,1,3-cyclohexadiene, n-heptane, 2-methylhexane, 3-methylhexane, n-octane,n-nonane, benzene, toluene, ethylbezene, m-xylene, o-xylene, p-xylene,styrene, dicyclopentadiene, and indane. Here, a content of C6 to C8hydrocarbons in the RPG stream may be 40 wt % or more, 45 wt % to 75 wt%, or 50 wt % to 70 wt %.

The RPG stream may be supplied to the BTX preparation process (S4) toprepare one or more of benzene, toluene, and xylene. For example, in theBTX preparation process (S4), benzene or BTX may be prepared. The BTX isan abbreviation of benzene, toluene, and xylene, and the xylene mayinclude ethyl benzene, m-xylene, o-xylene, and p-xylene.

According to an exemplary embodiment of the present invention, the PFOstream containing pyrolysis fuel oil (PFO) and the PGO stream containingpyrolysis gas oil (PGO) may be supplied to the distillation tower 50 asa feed stream, the PFO stream and the PGO stream being discharged in thenaphtha cracking center process (S1).

The feed stream supplied to the distillation tower 50 includes both thePGO stream and the PFO stream, and may contain both heavy oil (heavies)and light oil (lights). As such, the feed stream containing both theheavy oil and light oil is supplied to the distillation tower 50, andthe upper discharge stream containing a light PFO stream is dischargedfrom an upper portion of the distillation tower 50, such that a lowerdischarge stream having an adjusted kinematic viscosity and flash pointmay be discharged from a lower portion of the distillation tower 50. Asa specific example, the PFO stream having a higher content of heavy oilthan the PGO stream may have a higher kinematic viscosity and a higherflash point than the PGO stream, and the PGO stream having a highercontent of light oil than the PFO stream may have a lower kinematicviscosity and a lower flash point than the PFO stream. In the feedstream including both two conflicting streams, a stream having a desiredkinematic viscosity and flash point may be discharged from the lowerportion of the distillation tower 50 by removing the light oil, asdescribed above.

According to an exemplary embodiment of the present invention, the feedstream may be a mixed oil stream obtained by mixing the PFO stream andthe PGO stream. In this case, for example, a ratio of a flow rate of themixed oil stream to a flow rate of the PGO stream contained in the mixedoil stream (hereinafter, referred to as a “flow rate ratio of the PGOstream”) may be 0.35 to 0.7, 0.4 to 0.65, or 0.4 to 0.6, but is notlimited thereto. Here, the “flow rate” may refer to a flow of a weightper unit hour. As a specific example, a unit of the flow rate may bekg/h.

A boiling point of the mixed oil stream may be 200° C. to 600° C., 210°C. to 550° C., or 240° C. to 500° C. The boiling point of the mixed oilstream may refer to a boiling point of a mixed oil stream in a bulk formcomposed of a plurality of hydrocarbons.

According to an exemplary embodiment of the present invention, the mixedoil stream may pass through a first heat exchanger 40 before beingsupplied to the distillation tower 50, and then may be supplied to thedistillation tower 50. The mixed oil stream is produced by mixing thePGO stream and the PFO stream at a high temperature discharged from thefirst stripper 20 or the second stripper 30, and the temperature of themixed oil stream at the time of supply to the distillation tower 50 maybe optimally adjusted and also process energy may be reduced by reusingthe sensible heat of the mixed oil stream in the process, if necessary.

According to an exemplary embodiment of the present invention, the mixedoil stream may be supplied to a stage of 10% to 70%, 15% to 60%, or 20%to 50%, of the total number of stages of the distillation tower 50.Within this range, the distillation tower 50 may be efficientlyoperated, and unnecessary energy consumption may be significantlyreduced.

According to an exemplary embodiment of the present invention, a ratioof a flow rate of the feed stream supplied to the distillation tower 50to a flow rate of the upper discharge stream from the distillation tower50 (hereinafter, referred to as a “distillation ratio of thedistillation tower 50”) may be 0.01 to 0.2, 0.01 to 0.15, 0.03 to 0.15,or 0.1 to 0.2. That is, the distillation ratio of the distillation tower50 may be adjusted to 0.01 to 0.2, 0.01 to 0.15, or 0.03 to 0.15.

The distillation ratio of the distillation tower 50 in the above rangemay be adjusted by a flow rate adjustment device (not illustrated)installed in a pipe through which the upper discharge stream from thedistillation tower 50 is transported, and the performance of thedistillation tower 50 may be performed by adjusting a reflux ratio ofthe upper discharge stream from the distillation tower 50 using thedistillation ratio and a second heat exchanger 51. Here, the refluxratio may refer to a ratio of a flow rate of a reflux stream to a flowrate of an outflow stream, and as a specific example, the reflux ratioof the upper discharge stream from the distillation tower 50 may referto, when a part of the upper discharge stream from the distillationtower 50 is branched and refluxed to the distillation tower 50 as areflux stream and the rest is supplied to the BTX preparation process(S4) as an outflow stream, a ratio of a flow rate of the reflux streamto a flow rate of the outflow stream (hereinafter, referred to as a“reflux ratio”). As a more specific example, the reflux ratio may be0.01 to 10, 0.1 to 7, or 0.15 to 5.

A gasifying agent and a raw material may be supplied to the combustionchamber (not illustrated) positioned at the foremost end of thegasification process (S3) to produce synthesis gas by a combustionprocess at a temperature of 700° C. or higher. Here, the reaction ofproducing synthesis gas is performed under a high pressure of 20 to 80atm, and the raw material in the combustion chamber should be moved at ahigh flow velocity of 2 to 40 m/s. Therefore, the raw material should bepumped at a high flow velocity under a high pressure for the reaction ofproducing synthesis gas, and when a kinematic viscosity of the rawmaterial supplied to the combustion chamber is higher than anappropriate range, a high-priced pump should be used due to reducedpumpability or costs are increased due to increased energy consumption,and pumping may be impossible under desired conditions. In addition,since pumping is not smoothly performed, the raw material may not beuniformly supplied to the combustion chamber. In addition, since adifferential pressure in the combustion chamber is raised or uniformatomization of the raw material is not smoothly performed due to itssmall particle size, combustion performance may be deteriorated,productivity may be lowered, a large amount of the gasifying agent maybe required, and a risk of explosion may be increased due to excessiveoxygen. Here, an appropriate range of the kinematic viscosity may besomewhat different depending on the type of synthesis gas to besynthesized, conditions of the combustion process performed in thecombustion chamber, and the like. However, in general, a lower kinematicviscosity of the raw material is better in terms of costs, productivity,and safety, at a temperature of the raw material at the time of supplyto the combustion chamber in the gasification process (S3). Thekinematic viscosity may be preferably in a range of 300 cSt or less. Adifferential pressure rise in the combustion chamber is prevented withinthe range, and atomization is smoothly performed, such that combustionperformance may be improved and reactivity may be improved due to smoothcombustion reaction.

In addition, when a flash point of the raw material supplied to thecombustion chamber is lower than an appropriate range, a flame may occurin a burner before combustion reaction occurrence due to the low flashpoint, a risk of explosion may occur due to a backfire phenomenon of theflame in the combustion chamber, and the refractories in the combustionchamber may be damaged. Here, an appropriate range of the flash pointmay vary depending on the type of synthesis gas to be synthesized in thecombustion chamber, conditions of the combustion process performed inthe combustion chamber, and the like. However, in general, the flashpoint of the raw material may be preferably in a range of being higherthan the temperature of the raw material at the time of supply to thecombustion chamber in the gasification process (S3) by 25° C. or more,and within the range, a loss of the raw material, an explosion risk, anddamage of refractories in the combustion chamber may be prevented.

Accordingly, in the present invention, in order to control the kinematicviscosity and the flash point of the lower discharge stream from thedistillation tower 50 that is the raw material supplied to thecombustion chamber in the gasification process (S3) to appropriateranges, the distillation ratio of the distillation tower 50 may beadjusted. That is, by adjusting the distillation ratio of thedistillation tower 50, the kinematic viscosity and the flash point ofthe lower discharge stream from the distillation tower 50 may becontrolled to appropriate ranges, at a temperature when the lowerdischarge stream from the distillation tower 50 is supplied to thecombustion chamber. In addition, by adjusting the distillation ratio ofthe distillation tower 50, the composition in the upper discharge streamfrom the distillation tower 50 is controlled, and when the upperdischarge stream from the distillation tower 50 is supplied to the BTXpreparation process (S4), production of BTX may be increased.

According to an exemplary embodiment of the present invention, a thirdheat exchanger 52 may be operated as a general reboiler.

According to an exemplary embodiment of the present invention, thetemperature of the lower discharge stream from the distillation tower 50at the time of supply to the combustion chamber may be lower than theflash point of the lower discharge stream from the distillation tower 50at the time of supply to the combustion chamber by 25° C. or more, andmay be a temperature having a kinematic viscosity of 300 cSt or less.That is, the kinematic viscosity of the lower discharge stream of thedistillation tower 50 at the time of supply to the combustion chambermay be 300 cSt or less or 1 cSt to 300 cSt, and the flash point of thelower discharge stream of the distillation tower 50 may be higher thanthe temperature at the time of supply to the combustion chamber by 25°C. or more or 25° C. to 150° C. Here, the temperature of the lowerdischarge stream of the distillation tower 50 at the time of supply tothe combustion chamber may be 20° C. to 90° C. or 30° C. to 80° C. Thekinematic viscosity of the lower discharge stream from the distillationtower 50 at the temperature at the time of supply to the combustionchamber within the range may be 300 cSt or less and the temperature atthe time of supply to the combustion chamber may be further lower thanthe flash point by 25° C. or more, and thus, may satisfy the processoperating conditions for use as the raw material for the gasificationprocess (S3).

Specifically, by adjusting the distillation ratio of the distillationtower 50 to 0.01 to 0.2, 0.01 to 0.15, or 0.03 to 0.15, when the lowerdischarge stream from the distillation tower 50 is supplied to thecombustion chamber, the flash point of the lower discharge stream fromthe distillation tower 50 may be higher than the temperature of thelower discharge stream from the distillation tower 50 at the time ofsupply by 25° C. or more, and the kinematic viscosity thereof may be ina range of 300 cSt or less at the temperature of the lower dischargestream from the distillation tower 50 at the time of supply.

When the distillation ratio of the distillation tower 50 is 0.01 to 0.2,a light material having a low flash point is removed in the situationwhere both the flash point and the kinematic viscosity are low, suchthat an increase range of the flash point is more increased than anincrease range of the kinematic viscosity. Therefore, the flash pointand the kinematic viscosity when the lower discharge stream from thedistillation tower 50 is supplied to the combustion chamber may becontrolled to the ranges of the flash point and the kinematic viscositydescribed above. On the other hand, when the distillation ratio of thedistillation tower 50 is less than 0.01, it is difficult to control theflash point when the lower discharge stream from the distillation tower50 is supplied to the combustion chamber to be higher than thetemperature when the lower discharge stream from the distillation tower50 is supplied to the combustion chamber by 25° C. or more, and when thedistillation ratio of the distillation tower 50 is more than 0.2, theincrease range of the kinematic viscosity is more increased than theincrease range of the flash point, and thus, it is difficult to controlthe kinematic viscosity to 300 cSt or less.

As such, by adjusting the distillation ratio of the distillation tower50, the flash point and the kinematic viscosity of the lower dischargestream from the distillation tower 50 at the time of supply to thecombustion chamber may be controlled, and thus, the lower dischargestream from the distillation tower may have physical propertiesappropriate for use as the raw material for the gasification process(S3).

Meanwhile, for example, when the PFO stream is directly supplied to thecombustion chamber without the pretreatment process (S2) as illustratedin FIG. 2 , the PGO stream is directly supplied to the combustionchamber without the pretreatment process (S2) as illustrated in FIG. 3 ,or the mixed oil stream of the PGO stream and the PFO stream is directlysupplied to the combustion chamber without the pretreatment process (S2)according to the present invention as illustrated in FIG. 4 , atemperature satisfying both the kinematic viscosity and the flash pointin the appropriate ranges described above may not exist. As such, whenthe PFO stream, the PGO stream, or the mixed oil stream is supplied tothe combustion chamber at the temperature which does not satisfy any oneof the kinematic viscosity and the flash point in the appropriateranges, a differential pressure in the combustion chamber may be raisedor atomization may not be smoothly performed to deteriorate combustionperformance, and an explosion risk may be increased due to excessiveoxygen, or a flame may occur in the burner before combustion reactionoccurrence, and an explosion risk may be present due to a backfirephenomenon of the flame in the combustion chamber and refractories inthe combustion chamber may be damaged.

In general, the PFO stream and the PGO stream are the heaviest residuesin the NCC process and have been used as a simple fuel, and when theyare used as a simple fuel as such, it is not necessary to adjust thecompositions and the physical properties thereof. However, as in thepresent invention, in order to use the stream as the raw material of thesynthesis gas, specific physical properties, for example, both akinematic viscosity and a flash point should be satisfied. However, thePGO stream satisfies the kinematic viscosity but has a flash point thatis too low, and the PFO stream has a high flash point but has akinematic viscosity that is too high, and thus, each stream may notsatisfy both the kinematic viscosity and the flash point and it isdifficult to use each of the streams as the raw material of thesynthesis gas. In addition, in a case where the entire stream of the PFOstream and the PGO stream is used as the raw material of the synthesisgas, a ratio of the flow rate of the PGO stream to a flow rate of theentire stream of the PFO stream and the PGO stream is generally about0.35 to 0.7, and in this case also, the kinematic viscosity conditionfor use as the raw material for the gasification process at the flashpoint or lower may not be satisfied and it is difficult to use thestream as the raw material of the synthesis gas. In this regard, in thepresent invention, the entire amount of the PFO stream and the PGOstream is supplied to the distillation tower 50 and pretreated, suchthat when the lower discharge stream from the distillation tower 50 issupplied to the combustion chamber, the flash point of the lowerdischarge stream from the distillation tower 50 may be controlled to arange higher than the temperature of the lower discharge stream from thedistillation tower 50 at the time of supply by 25° C. or more, and thekinematic viscosity may also be controlled to a range of 300 cSt or lessat the temperature of the lower discharge stream from the distillationtower 50 at the time of supply, and thus, the conditions for use thestream as the raw material of the synthesis gas may be satisfied.

According to an exemplary embodiment of the present invention, the lowerdischarge stream from the distillation tower 50 may pass through afourth heat exchanger 53 before being supplied to the gasificationprocess (S3), and then may be supplied to the gasification process (S3).In this case, the temperature of the lower discharge stream from thedistillation tower 50 at the time of supply to gasification process (S3)may be adjusted and also process energy may be reduced by reusing thesensible heat of the lower discharge stream from the distillation tower50 which may be wasted as waste heat in the process using the heatexchanger.

According to an exemplary embodiment of the present invention, the upperdischarge stream from the distillation tower 50 may be supplied to theBTX preparation process (S4) to prepare aromatic hydrocarbons.

According to an exemplary embodiment of the present invention, the lowerdischarge stream from the distillation tower 50 may have a content ofC10+ hydrocarbons of 80 wt % or more or 80 wt % to 98 wt % and a contentof C8− hydrocarbons of 5 wt % or less or 0.01 wt % to 5 wt %, and theupper discharge stream from the distillation tower 50 may have a contentof C6 to C8 aromatic hydrocarbons of 50 wt % or more, 55 wt % to 95 wt%, or 55 wt % to 85 wt %.

For example, the C8− hydrocarbon may include one or more selected fromthe group consisting of pentane, pentene, pentadiene, methylbutene,cyclopentane, cyclopentene, hexane, cyclohexane, heptane, methylhexane,octane, benzene, toluene, xylene, and styrene. As a specific example,the C8− hydrocarbon may include all types of C8− hydrocarbons describedabove, but the present invention is not limited thereto.

In addition, for example, the C10+ hydrocarbon may include one or moreselected from the group consisting of dicyclopentadiene, naphthalene,methylnaphthalene, tetramethylbenzene, fluorene, and anthracene. As aspecific example, the C10+ hydrocarbon may include all types of C10+hydrocarbons described above, but the present invention is not limitedthereto.

In addition, for example, the C6 to C8 aromatic hydrocarbons may includeone or more selected from the group consisting of benzene, toluene,xylene, and styrene. As a specific example, the C6 to C8 aromatichydrocarbons may include all types of C6 to C8 aromatic hydrocarbonsdescribed above, but the present invention is not limited thereto.

As such, the lower discharge stream from the distillation tower 50 isused as the raw material of synthesis gas, and the upper dischargestream from the distillation tower 50 in which the content of the C6 toC8 aromatic hydrocarbons is 50 wt % or more is supplied to the BTXpreparation process (S4), such that the pyrolysis fuel oil may be usedas the raw material for the gasification process, and the aromatichydrocarbons in the pyrolysis fuel oil may be recovered to increaseproduction of benzene, toluene, and xylene.

According to an exemplary embodiment of the present invention, burningthe lower discharge stream from the distillation tower 50 supplied tothe combustion chamber in the gasification process (S3) at a temperatureof 700° C. or higher, 700° C. to 2,000° C., or 800° C. to 1,800° C. maybe further included. In addition, the lower discharge stream from thedistillation tower 50 may be supplied to the combustion chamber togetherwith the gasifying agent. Here, the gasifying agent may include one ormore selected from the group consisting of oxygen, air, and water vapor,and as a specific example, the gasifying agent may be oxygen or watervapor.

As such, the lower discharge stream from the distillation tower 50 isburned at a high temperature in the presence of the gasifying agent,such that the synthesis gas may be prepared. The synthesis gas preparedaccording to the preparation method of the present invention containscarbon monoxide and hydrogen and may further contain one or moreselected from the group consisting of carbon dioxide, ammonia, hydrogensulfide, hydrogen cyanide, and carbonyl sulfide.

According to an exemplary embodiment of the present invention, the upperdischarge stream from the distillation tower 50 may be supplied to theBTX preparation process (S4) together with the RPG stream, and one ormore selected from the group consisting of benzene, toluene, and xylenemay be prepared.

According to an exemplary embodiment of the present invention, the upperdischarge stream from the distillation tower is supplied to ahydrodesulfurization unit in the BTX preparation process (S4) togetherwith the RPG stream to cause hydrodesulfurization in the presence ofseparately supplied hydrogen and a catalyst. The catalyst may be acatalyst capable of selective hydrogenation. For example, the catalystmay include one or more selected from the group consisting of palladium,platinum, copper, and nickel. In some cases, the catalyst may be used bybeing supported on one or more carriers selected from the groupconsisting of gamma alumina, activated carbon, and zeolite.

A discharge stream from the hydrodesulfurization unit may be supplied toa C5 separation column. An upper discharge stream containing C5−aromatic hydrocarbons may be discharged from the C5 separation column,and a lower discharge stream containing C6+ aromatic hydrocarbons may besupplied to a C7 separation column.

An upper discharge stream containing C7− aromatic hydrocarbons may besupplied from the C7 separation column to an extractive distillationcolumn, and a lower discharge stream containing C8+ aromatichydrocarbons may be supplied to a xylene separation column.

In the extractive distillation column, aromatic hydrocarbons andnon-aromatic hydrocarbons contained in the upper discharge stream fromthe C7 separation column may be separated using an extraction solvent.Specifically, in the extractive distillation column, the aromatichydrocarbons contained in the upper discharge stream from the C7separation column may be selectively extracted and separated as a lowerdischarge stream, and the non-aromatic hydrocarbons may be separated asan upper discharge stream. For example, the extraction solvent mayinclude one or more selected from the group consisting of sulfolane,alkyl-sulfolane, N-formylmorpholine, N-methylpyrrolidone, tetraethyleneglycol, triethylene glycol, and diethylene glycol. In addition, theextraction solvent may further include water as a co-solvent.

The lower discharge stream from the extractive distillation columncontains C7− aromatic hydrocarbons, and may be supplied to a benzeneseparation column to separate benzene from an upper discharge streamfrom the benzene separation column, and a lower discharge stream fromthe benzene separation column may be supplied to a toluene separationcolumn. Here, the lower discharge stream from the extractivedistillation column supplied to the benzene separation column may besupplied to a solvent recovery column for removing the extractionsolvent and then may be supplied to the benzene separation column.

The lower discharge stream from the benzene separation column containsC7 aromatic hydrocarbons, and may be supplied to the toluene separationcolumn to separate toluene from an upper discharge stream from thetoluene separation column, and a lower discharge stream from the tolueneseparation column may be supplied to a xylene separation column.

The lower discharge stream from the C7 separation column and the lowerdischarge stream from the toluene separation column may be supplied tothe xylene separation column to separate xylene from an upper dischargestream, and the rest C9+ hydrocarbon heavy substances may be dischargedfrom a bottom portion.

According to an exemplary embodiment of the present invention, in themethod for preparing synthesis gas and aromatic hydrocarbons, ifnecessary, devices such as a valve, a pump, a separator, and a mixer maybe further installed.

Hereinabove, the method for preparing synthesis gas and aromatichydrocarbons according to the present invention has been described andillustrated in the drawings, but the description and the illustration inthe drawings are the description and the illustration of only coreconstitutions for understanding of the present invention, and inaddition to the process and devices described above and illustrated inthe drawings, the process and the devices which are not described andillustrated separately may be appropriately applied and used forcarrying out the method for preparing synthesis gas and aromatichydrocarbons according to the present invention.

Hereinafter, the present invention will be described in more detail byExamples. However, the following Examples are provided for illustratingthe present invention. It is apparent to those skilled in the art thatvarious modifications and alterations may be made without departing fromthe scope and spirit of the present invention, and the scope of thepresent invention is not limited thereto.

EXAMPLES Examples 1 to 5

According to the process flow diagram illustrated in FIG. 1 , BTX andsynthesis gas were prepared.

Specifically, an upper discharge stream discharged at a stage of 1% ofthe total number of stages of a gasoline fractionator 10 in a naphthacracking center process (S1) was supplied to an NCC subsequent process(not illustrated), and an RPG stream was discharged in the NCCsubsequent process. In addition, a side discharge stream discharged at astage of 40% of the total number of stages of the gasoline fractionator10 was supplied to a first stripper 20, and then a pyrolysis gas oil(PGO) stream containing PGO was discharged from a lower portion of thefirst stripper 20, and at this time, it was confirmed that a content ofC10 to C12 hydrocarbons in the PGO stream was 86 wt %. In addition, alower discharge stream discharged at a stage of 100% of the total numberof stages of the gasoline fractionator 10 was supplied to a secondstripper 30, and then a pyrolysis fuel oil (PFO) stream containing PFOwas discharged from a lower portion of the second stripper 30, and atthis time, it was confirmed that a content of C13+ hydrocarbons in thePFO stream was 89 wt %. In addition, the PGO stream had a flash point of25.5° C. and a kinematic viscosity at 40° C. of 75 cSt, and the PFOstream had a flash point of 98° C. and a kinematic viscosity at 40° C.of 660 cSt.

A mixed oil stream obtained by mixing the PGO stream and the PFO streamwas supplied to a distillation tower 50, and then, a distillation ratioof the distillation tower 50 was adjusted and an upper discharge streamfrom the distillation tower 50 was discharged, and a lower dischargestream from the distillation tower 50 was supplied to a combustionchamber in a gasification process (S3) together with oxygen and vapor,thereby preparing synthesis gas containing hydrogen and carbon monoxide.At this time, a ratio of a flow rate of the PGO stream to a flow rate ofthe mixed oil stream was 0.42, and the mixed oil stream had a flashpoint of 70° C. and a kinematic viscosity at 40° C. of 365 cSt. Inaddition, a reflux ratio of the mixed oil stream from the distillationtower 50 was adjusted to 2.5.

An RPG mixed stream obtained by mixing the RPG stream and the upperdischarge stream from the distillation tower 50 was supplied to a BTXpreparation process (S4) to prepare benzene, toluene, and xylene using ahydrodesulfurization unit, a C5 separation column, a C7 separationcolumn, an extractive distillation column, a benzene separation column,a toluene separation column, and a xylene separation column.

The content ratios of the C6 to C8 aromatic hydrocarbons in the lowerdischarge stream and the upper discharge stream from the distillationtower 50, the distillation ratio of the distillation tower 50, and thetemperature and the flash point of the lower discharge stream from thedistillation tower 50 at the time of supply to the combustion chamberwere measured. The results are shown in Table 1. In addition, it wasconfirmed whether the process operating standards were satisfiedaccording to the measurement results. At this time, the time when thelower discharge stream from the distillation tower 50 was supplied tothe combustion chamber was set to temperature conditions to control thekinematic viscosity to 300 cSt using a fourth heat exchanger 53.Specifically, in order to derive the temperature conditions to controlthe kinematic viscosity to 300 cSt, the kinematic viscosity of thecorresponding sample was measured by temperature, and then, acorrelation between the temperature and the viscosity was establishedand calculated using interpolation.

In addition, the production of benzene, toluene, and xylene produced inthe BTX preparation process (S4) is shown in Table 3.

The kinematic viscosity and the flash point were measured as follows,and were applied to all of Examples and Comparative Examples.

(1) Kinematic viscosity: A sample was obtained from the stream of thesample to be measured and measurement was performed based on ASTM D7042using SVM 3001 available from Anton Paar. In addition, the temperatureof each of the samples was maintained at a temperature lower than akinematic viscosity measurement temperature by 10° C., and the samplewas stored in a closed container for preventing vaporization of lightmaterials to minimize occurrence of a gas phase.

(2) Flash point: A sample was obtained from the stream of the sample tobe measured and measurement was performed based on ASTM D93 using apm-8available from TANAKA. In addition, the temperature of each of thesamples was maintained at a temperature lower than an expected flashpoint by 10° C., and the sample was stored in a closed container forpreventing vaporization of light materials to minimize occurrence of agas phase.

COMPARATIVE EXAMPLES Comparative Example 1

According to the process flow diagram illustrated in FIG. 2 , synthesisgas was prepared.

Specifically, the lower discharge stream discharged at the stage of 100%of the total number of stages of the gasoline fractionator 10 in thenaphtha cracking center process (S1) was supplied to the second stripper30, and the pyrolysis fuel oil (PFO) stream containing PFO wasdischarged from the lower portion of the second stripper 30.

The PFO stream was supplied to the combustion chamber in thegasification process (S3) together with oxygen and vapor. At this time,it was confirmed that the content of C13+ in the PFO stream was 89 wt %,and the PFO stream had a flash point of 98° C. and a kinematic viscosityat 40° C. of 660 cSt.

In addition, the upper discharge stream discharged at the stage of 1% ofthe total number of stages of the gasoline fractionator 10 in thenaphtha cracking center process (S1) was supplied to the NCC subsequentprocess (not illustrated), the RPG stream was discharged in the NCCsubsequent process, and the RPG stream was supplied to the BTXpreparation process (S4), thereby preparing benzene, toluene, and xyleneusing the hydrodesulfurization unit, the C5 separation column, the C7separation column, the extractive distillation column, the benzeneseparation column, the toluene separation column, and the xyleneseparation column.

The temperature of the PFO stream at the time of supply to thecombustion chamber was measured. The result is shown in Table 2. Inaddition, it was confirmed whether the process operating standards weresatisfied according to the measurement results. At this time, the timewhen the PFO stream was supplied to the combustion chamber was set totemperature conditions to control the kinematic viscosity to 300 cStusing the heat exchanger.

In addition, the production of benzene, toluene, and xylene produced inthe BTX preparation process (S4) is shown in Table 3.

Comparative Example 2

According to the process flow diagram illustrated in FIG. 3 , synthesisgas was prepared.

Specifically, the side discharge stream discharged at the stage of 40%of the total number of stages of the gasoline fractionator 10 in thenaphtha cracking center process (S1) was supplied to the first stripper20, and the pyrolysis gas oil (PGO) stream containing PGO was dischargedfrom the lower portion of the first stripper 20.

The PGO stream was supplied to the combustion chamber in thegasification process (S3) together with oxygen and vapor. At this time,it was confirmed that the content of C10 to C12 in the PGO stream was 86wt %, and the PGO stream had a flash point of 25.5° C. and a kinematicviscosity at 40° C. of 75 cSt.

In addition, the upper discharge stream discharged at the stage of 1% ofthe total number of stages of the gasoline fractionator 10 in thenaphtha cracking center process (S1) was supplied to the NCC subsequentprocess (not illustrated), the RPG stream was discharged in the NCCsubsequent process, and the RPG stream was supplied to the BTXpreparation process (S4), thereby preparing benzene, toluene, and xyleneusing the hydrodesulfurization unit, the C5 separation column, the C7separation column, the extractive distillation column, the benzeneseparation column, the toluene separation column, and the xyleneseparation column.

The temperature of the PGO stream at the time when the PGO stream wassupplied to the combustion chamber was measured. The result is shown inTable 2. In addition, it was confirmed whether the process operatingstandards were satisfied according to the measurement results. At thistime, the time when the PGO stream was supplied to the combustionchamber was set to temperature conditions to control the kinematicviscosity to 300 cSt using the heat exchanger.

In addition, the production of benzene, toluene, and xylene produced inthe BTX preparation process (S4) is shown in Table 3.

Comparative Example 3

According to the process flow diagram illustrated in FIG. 4 , synthesisgas was prepared.

Specifically, the side discharge stream discharged at the stage of 40%of the total number of stages of the gasoline fractionator 10 in thenaphtha cracking center process (S1) was supplied to the first stripper20, and then the pyrolysis gas oil (PGO) stream containing PGO wasdischarged from the lower portion of the first stripper 20, and at thistime, it was confirmed that a content of C10 to C12 in the PGO streamwas 86 wt %. In addition, the lower discharge stream discharged at thestage of 100% of the total number of stages of the gasoline fractionator10 was supplied to the second stripper 30, and then the pyrolysis fueloil (PFO) stream containing PFO was discharged from the lower portion ofthe second stripper 30, and at this time, it was confirmed that acontent of C13+ in the PFO stream was 89 wt %.

Next, a mixed oil stream was produced by mixing the PGO stream and thePFO stream. At this time, the PGO stream had a flash point of 25.5° C.and a kinematic viscosity at 40° C. of 75 cSt, and the PFO stream had aflash point of 98° C. and a kinematic viscosity at 40° C. of 660 cSt. Inaddition, a ratio of a flow rate of the PGO stream to a flow rate of themixed oil stream was 0.42. Then, the mixed oil stream was supplied tothe combustion chamber in the gasification process (S3) together withoxygen and vapor.

In addition, the upper discharge stream discharged at the stage of 1% ofthe total number of stages of the gasoline fractionator 10 in thenaphtha cracking center process (S1) was supplied to the NCC subsequentprocess (not illustrated), the RPG stream was discharged in the NCCsubsequent process, and the RPG stream was supplied to the BTXpreparation process (S4), thereby preparing benzene, toluene, and xyleneusing the hydrodesulfurization unit, the C5 separation column, the C7separation column, the extractive distillation column, the benzeneseparation column, the toluene separation column, and the xyleneseparation column.

The flash point of the mixed oil stream and the temperature when themixed oil stream was supplied to the combustion chamber were measured.The results are shown in Table 2. In addition, it was confirmed whetherthe process operating standards were satisfied according to themeasurement results. At this time, the time when the mixed oil streamwas supplied to the combustion chamber was set to temperature conditionsto control the kinematic viscosity to 300 cSt using the heat exchanger.

In addition, the production of benzene, toluene, and xylene produced inthe BTX preparation process (S4) is shown in Table 3.

Comparative Example 4

Synthesis gas and aromatic hydrocarbons were prepared in the same manneras that of Example 1, except that the upper discharge stream from thedistillation tower 50 was not supplied to the BTX preparation process(S4) in Example 1.

In addition, the production of benzene, toluene, and xylene produced inthe BTX preparation process (S4) is shown in Table 3.

TABLE 1 Kinematic Temperature viscosity Ratio of C6 to C8 of lower oflower Flash Whether aromatic discharge discharge point of processhydrocarbons stream at stream at lower operating Upper Lower time oftime of discharge standards Distillation discharge discharge supplysupply stream are ratio stream stream (° C.) (cSt) (° C.) satisfiedExample 0.005 0 1 48.3 300 73 X 1 Example 0.01 0.08 0.92 49.2 300 75 ◯ 2Example 0.1 1 0 60 300 90.5 ◯ 3 Example 0.2 1 0 73.3 300 99 ◯ 4 Example0.3 1 0 97.6 300 105.5 X 5

TABLE 2 Kinematic Whether viscosity of Temperature process Flash pointstream at of stream operating of stream time of at time of standards are(° C.) supply (cSt) supply (° C.) satisfied Comparative 98 300 78 XExample 1 (PFO) Comparative 25.5 300 14 X Example 2 (PGO) Comparative 70300 47 X Example 3 (Mixed oil)

TABLE 3 Production Production Production of benzene of toluene of xylene(%) (%) (%) Example 1 100.0 100.0 100.0 Example 2 100.1 100.1 100.0Example 3 100.2 100.8 109.3 Example 4 100.2 100.8 109.3 Example 5 100.2100.8 109.3 Comparative 100.0 100.0 100.0 Example 1 Comparative 100.0100.0 100.0 Example 2 Comparative 100.0 100.0 100.0 Example 3Comparative 100.0 100.0 100.0 Example 4

In Tables 1 and 2, whether the process operating standards weresatisfied was indicated by 0 when the temperature at the time when thestream supplied to the combustion chamber in each of Examples 1 to 5 andComparative Examples 1 to 3 was supplied to the combustion chamber atwhich the kinematic viscosity at the time of supply to the combustionchamber was 300 cSt was lower than the flash point by 25° C. or more,and was indicated by X when the temperature did not satisfy theabove-described condition.

In addition, in Table 3, the production of each of benzene, toluene, andxylene was expressed as a relative production ratio of each of benzene,toluene, and xylene calculated based on the production (100%) of each ofbenzene, toluene, and xylene in Comparative Example 1.

Referring to Tables 1 and 2, in Examples 2 to 4 in which according tothe method for preparing synthesis gas of the present invention, thedistillation ratio of the distillation tower 50 was adjusted to theappropriate range (0.01 to 0.2) to produce the lower discharge stream,and the lower discharge stream from the distillation tower 50 wassupplied to the combustion chamber for the gasification process (S3), itcould be confirmed that when the lower discharge stream from thedistillation tower 50 was supplied to the combustion chamber, the flashpoint of the lower discharge stream from the distillation tower 50 washigher than the temperature of the lower discharge stream from thedistillation tower 50 at the time of supply to the combustion chamber by25° C. or more, and the kinematic viscosity thereof was in a range of300 cSt or less at the temperature of the lower discharge stream fromthe distillation tower 50 at the time of supply to the combustionchamber. It was confirmed that since both the flash point and thekinematic viscosity were in the ranges as such, the process operatingconditions for use as the raw material for the gasification process (S3)were satisfied.

In particular, as illustrated in FIG. 1 , in Example 3 in which thedistillation ratio of the distillation tower 50 in the pretreatmentprocess (S2) was controlled to a range of 0.03 to 0.15, it was confirmedthat when the lower discharge stream from the distillation tower 50 wassupplied to the combustion chamber, the flash point of the lowerdischarge stream from the distillation tower 50 was higher than thetemperature of the lower discharge stream from the distillation tower 50at the time of supply to the combustion chamber by 30° C. or more toallow more stable operation.

In addition, in Examples 1 to 5 in which the lower discharge stream tobe discharged from the distillation tower 50 was formed in the statewhere the distillation ratio of the distillation tower 50 was notadjusted to the appropriate range (0.01 to 0.2), it was appreciated thatwhen the kinematic viscosity at the temperature of the lower dischargestream from the distillation tower 50 at the time of supply to thecombustion chamber was controlled to 300 cSt, the temperature of thelower discharge stream from the distillation tower 50 at the time ofsupply to the combustion chamber was not controlled to be lower than theflash point by 25° C. or more.

On the other hand, when the PFO stream was directly supplied to thecombustion chamber without the pretreatment process (S2) as illustratedin FIG. 2 (Comparative Example 1), the PGO stream was directly suppliedto the combustion chamber without the pretreatment process (S2) asillustrated in FIG. 3 (Comparative Example 2), or the mixed oil streamof the PGO stream and the PFO stream was directly supplied to thecombustion chamber without the pretreatment process (S2) according tothe present invention as illustrated in FIG. 4 (Comparative Example 3),it could be confirmed that a temperature satisfying both the kinematicviscosity and the flash point in the appropriate ranges described abovedid not exist. As such, it was confirmed that each of the streams ofComparative Examples 1 to 3 which did not satisfy both the kinematicviscosity and the flash point in the appropriate ranges did not satisfythe process operating conditions for use as the raw material for thegasification process (S3).

When the raw material for the gasification process (S3) is supplied tothe combustion chamber at the temperature which does not satisfy any oneof the kinematic viscosity and the flash point in the appropriateranges, a differential pressure in the combustion chamber may be raisedor atomization may not be smoothly performed to deteriorate combustionperformance, and an explosion risk may be increased due to excessiveoxygen, or a flame may occur in the burner before combustion reactionoccurrence, and an explosion risk may be present due to a backfirephenomenon of the flame in the combustion chamber and refractories inthe combustion chamber may be damaged.

In addition, referring to Table 3, it can be confirmed that in Examples1 to 5, the production of benzene, toluene, or xylene in the BTXpreparation process (S4) varies depending on the distillation ratio ofthe distillation tower 50, and the production is increased compared toComparative Examples. Specifically, it could be confirmed that when thedistillation ratio of the distillation tower 50 was controlled to 0.01or more, the C6 to C8 aromatic hydrocarbons were discharged through theupper discharge stream of the distillation tower 50, and in particular,when the distillation ratio of the distillation tower 50 was 0.1 ormore, the entire amount of the C6 to C8 aromatic hydrocarbons wasdischarged through the upper portion of the distillation tower 50.Therefore, it could be confirmed that controlling the distillation ratioof the distillation tower 50 to 0.1 to 0.2 was the optimal processcondition for preparing BTX together with synthesis gas.

1. A method for preparing synthesis gas and aromatic hydrocarbons, themethod comprising: supplying a pyrolysis fuel oil (PFO) streamcontaining PFO and a pyrolysis gas oil (PGO) stream containing PGO to adistillation tower as a feed stream (S10), the PFO stream and the PGOstream being discharged from a naphtha cracking center (NCC) process;and supplying a lower discharge stream from the distillation tower to acombustion chamber for a gasification process to obtain synthesis gasand supplying an upper discharge stream from the distillation tower to apreparation process of one or more of benzene, toluene, and xylene (BTXpreparation process) to obtain aromatic hydrocarbons (S20).
 2. Themethod of claim 1, wherein a ratio of a flow rate of the upper dischargestream from the distillation tower to a flow rate of the feed stream tobe supplied to the distillation tower is 0.01 to 0.2.
 3. The method ofclaim 1, wherein a ratio of a flow rate of the upper discharge streamfrom the distillation tower to a flow rate of the feed stream to besupplied to the distillation tower is 0.1 to 0.2.
 4. The method of claim1, wherein a kinematic viscosity of the lower discharge stream from thedistillation tower at the time of supply to the combustion chamber is300 cSt or less, and wherein a flash point of the lower discharge streamfrom the distillation tower is higher than a temperature of the lowerdischarge stream from the distillation tower at the time of supply tothe combustion chamber by 25° C. or more.
 5. The method of claim 1,wherein a temperature of the lower discharge stream from thedistillation tower at the time of supply to the combustion chamber is20° C. to 90° C.
 6. The method of claim 1, wherein the lower dischargestream from the distillation tower passes through a heat exchangerbefore being supplied to the combustion chamber.
 7. The method of claim1, wherein the PGO stream contains 70 wt % or more of hydrocarbonshaving 10-12 carbon atoms, and wherein the PFO stream contains 70 wt %or more of hydrocarbons having 13 or more carbon atoms.
 8. The method ofclaim 1, wherein a flash point of the PGO stream is 10 to 50° C., andwherein a flash point of the PFO stream is 70 to 200° C.
 9. The methodof claim 1, wherein a kinematic viscosity of the PGO stream at 40° C. is1 to 200 cSt, and wherein a kinematic viscosity of the PFO stream at 40°C. is 400 to 100,000 cSt.
 10. The method of claim 1, wherein a rawpyrolysis gasoline (RPG) stream containing RPG discharged from thenaphtha cracking center (NCC) process is supplied to the BTX preparationprocess.
 11. The method of claim 1, wherein the PGO stream is a lowerdischarge stream discharged from a lower portion of a first stripperafter supplying a side discharge stream discharged from a side portionof a gasoline fractionator in the naphtha cracking center (NCC) processto the first stripper, and wherein the PFO stream is a lower dischargestream discharged from a lower portion of a second stripper aftersupplying a lower discharge stream discharged from a lower portion ofthe gasoline fractionator in the naphtha cracking center (NCC) processto the second stripper.
 12. The method of claim 11, wherein the lowerdischarge stream from the gasoline fractionator is discharged at a stageof 90% or more of a total number of stages of the gasoline fractionator,and wherein the side discharge stream from the gasoline fractionator isdischarged at a stage of 10% to 70% of the total number of stages of thegasoline fractionator.
 13. The method of claim 1, wherein a reflux ratioof the distillation tower is 0.01 to 10.